A method for designing parameters of a compact oil reservoir energy storage fracturing process

Abstract

The application provides a method for designing parameters of energy storage fracturing technology in tight oil reservoirs, which combines laboratory experiments and numerical simulation to upgrade the design of parameters of energy storage fracturing technology in tight oil reservoirs from an empirical stage to a quantitative design stage. The application in key wells of tight oil reservoirs in Jiangsu oilfield has achieved good oil increasing effect, which proves that the method of first supplementing formation energy, then implementing large-scale sand fracturing and matching temporary plugging and steering technology, improving fracture complexity and reconstruction volume, can effectively prolong the fracturing oil increasing and stable production period. Meanwhile, the oil-water displacement between the original injected active water and formation crude oil can obviously improve the recovery rate, which provides a new way for effective reconstruction of difficult-to-produce reserves and yield increase and benefit improvement of old oil wells. Through quantitative simulation design, the whole construction parameters are more scientific and reasonable.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development technology, and specifically relates to a method for designing process parameters for energy storage fracturing in tight oil reservoirs. Background Technology

[0002] Tight oil reservoirs have poor reservoir properties and low natural well productivity. Conventional fracturing and volumetric fracturing techniques are generally used to improve single-well productivity. Although these techniques have achieved some improvement, they also present problems such as rapid initial production decline after fracturing, low and stable production levels, difficulties in water injection, and insufficient formation energy. To address these issues, a fracturing method that replenishes formation energy—energy storage fracturing—has emerged.

[0003] Compared to traditional hydraulic fracturing, energy storage fracturing increases formation stimulation volume while replenishing formation energy. Through appropriate well shut-in, it utilizes percolation to exchange crude oil within the formation matrix with fracturing fluid in the fractures, significantly improving oil recovery. Field application results of energy storage fracturing show that single-well production is 8-10 times higher than that of typical vertical wells and 2-3 times higher than that of other horizontal wells in the same production block.

[0004] Existing technologies only disclose the field implementation methods of energy storage fracturing for different reservoirs. However, process parameters such as the amount of energy storage fracturing fluid used, the discharge rate, and the well simmering time directly affect the post-fracturing effect. Therefore, it is necessary to establish a design method for energy storage fracturing process parameters. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a method for designing process parameters for energy storage fracturing in tight oil reservoirs, which solves the problem of insufficient design methods for process parameters such as fluid usage, discharge rate, and well shut-in time during energy storage fracturing in tight oil reservoirs.

[0006] This application provides a method for designing process parameters for energy storage fracturing in tight oil reservoirs, including:

[0007] S1. Obtain basic data of the target reservoir;

[0008] S2. Conduct indoor experiments to evaluate the performance of energy storage fracturing fluid;

[0009] S3. Determine the numerical simulation optimization scheme for process parameters;

[0010] S4. Simulation of pressurized seepage during fracture propagation in energy storage fracturing;

[0011] S5. Simulation of post-fracturing well sumption and production in energy storage fracturing;

[0012] S6. Determine the target process parameters based on production capacity;

[0013] S7. Repeat steps S4 to S6 until all target process parameters are determined.

[0014] The basic data of the target reservoir in step S1 include: porosity, permeability, oil saturation, crude oil viscosity, reservoir thickness, formation pressure coefficient, maximum horizontal principal stress, minimum horizontal principal stress, rock elastic model, Poisson's ratio, tensile strength, and wetting contact angle.

[0015] Among them, the performance parameters of the energy storage fracturing fluid in step S2 include surface / interfacial tension, wetting properties, permeability damage rate, and oil displacement capacity;

[0016] Among these methods, surface tension was measured using a fully automated surface tension meter, and interfacial tension between the stored fracturing fluid and dehydrated crude oil was measured using a rotary titration interfacial tension meter. In the wetting performance evaluation experiment, the core was directly immersed in the stored fracturing fluid, dried, and the wetting contact angle was directly measured. The wetting contact angle before and after immersion was compared, and the change rate of the contact angle was calculated. In the permeability damage rate experiment, the permeability of the core was first measured by gas, then the core was displaced with stored fracturing fluid, and finally the permeability of the core was measured by gas again. The permeability damage rate was obtained by comparing the permeability before and after displacement. In the oil displacement capacity experiment, the basic data of the core was first measured, and the core was saturated with standard brine, then saturated with dehydrated kerosene, and finally displaced with stored fracturing fluid until the water content of the produced fluid reached more than 98%.

[0017] The requirements are met when the surface tension of the energy storage fracturing fluid is <50mN / m, the interfacial tension is <0.1mN / m, the contact angle change rate is >35%, the permeability damage rate is <30%, and the displacement recovery rate is >5%.

[0018] In step S3, the process parameters include the amount of energy storage fracturing fluid used, the discharge rate, and the well-keeping time. During the numerical simulation, the target parameters are determined sequentially according to the order of energy storage fracturing fluid used, discharge rate, and well-keeping time. Specifically: set the discharge rate and well-keeping time, vary the amount of energy storage fracturing fluid used, and determine the optimal amount of energy storage fracturing fluid used; set the target amount of energy storage fracturing fluid used and the well-keeping time, vary the discharge rate, and determine the target discharge rate; set the target amount of energy storage fracturing fluid used and the target discharge rate, vary the well-keeping time, and determine the target well-keeping time.

[0019] In step S4, the method for simulating crack propagation is the element splitting method.

[0020] In step S4, the fracturing fluid absorption process during fracture propagation is pressurized absorption. The forces acting on the fracturing fluid in the matrix pores are capillary force, viscous resistance, and gravity. According to the force balance, its absorption rate is:

[0021]

[0022] In the formula: This is the absorption rate, expressed in m / s; The viscosity of the energy storage fracturing fluid is expressed in Pa·s. The pore radius is in meters (m). Interfacial tension, in N / m; The wetting contact angle is expressed in rad. The pressure difference between the inside and outside of the capillary tube; Density of the energy storage fracturing fluid, in kg / m³ 3 ; This is the acceleration due to gravity, measured in m / s². 2 , The height of the fracturing fluid drawn into the capillary is expressed in meters (m).

[0023] In step S4, the adsorption rate at different locations can be calculated based on the matrix pore pressure distribution and reservoir parameters during the fracture propagation process. The adsorption rate affects the matrix pore pressure distribution, so iterative solution is required to obtain the matrix pore pressure distribution at different times and after the fracture propagation ends.

[0024] In step S4, the crack conductivity is further calculated using the cubic law based on the crack width parameter after the crack propagation simulation.

[0025] In step S5, CMG software is used to establish a mechanism model to simulate the entire process of well simmering and production after energy storage fracturing. The initial pore pressure and fracture conductivity required in the calculation process are the pore pressure distribution and fracture conductivity after the fracture propagation is completed, as calculated in step S4.

[0026] The method for designing process parameters for energy storage fracturing in tight oil reservoirs according to the embodiments of this application has the following beneficial effects:

[0027] This invention combines indoor experiments and numerical simulations to elevate the design of energy storage fracturing process parameters in tight oil reservoirs from an empirical stage to a quantitative design stage. Its application in key wells of tight oil reservoirs in Jiangsu Oilfield has yielded significant oil enhancement results. It demonstrates that replenishing formation energy before implementing large-scale sand fracturing with a temporary plugging and diversion technique, increasing fracture complexity and stimulation volume, can effectively extend the stable production period of fracturing-induced oil production. Simultaneously, the previously injected active water-based washing agent undergoes oil-water exchange with the formation crude oil, significantly improving recovery rates. This provides a new approach for the effective stimulation of difficult-to-access reserves and for increasing production and efficiency in old oil wells. Through quantitative simulation design, the entire construction parameters are made more scientific and reasonable, filling a gap in related domestic fields. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process parameter design method for tight oil reservoir energy storage fracturing in an embodiment of this application;

[0029] Figure 2 The matrix pore pressure after the completion of energy storage fracturing operation;

[0030] Figure 3 The cumulative oil production over three years under different amounts of energy storage fracturing fluid;

[0031] Figure 4 Three-year cumulative oil production under different construction displacements;

[0032] Figure 5 The cumulative oil production over three years under different well-sinking times. Detailed Implementation

[0033] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0034] The following description provides several embodiments of the present invention. Different embodiments can be substituted or combined. Therefore, this application can also be considered to include all possible combinations of the same and / or different embodiments described. Thus, if one embodiment includes features A, B, and C, and another embodiment includes features B and D, then this application should also be considered to include embodiments containing one or more other possible combinations of A, B, C, and D, even if such embodiments are not explicitly described in the following text.

[0035] Example 1

[0036] The method for designing process parameters for energy storage fracturing in tight oil reservoirs in this application includes: S1. Obtaining basic data of the target reservoir; S2. Conducting laboratory experiments to evaluate the performance of energy storage fracturing fluid; S3. Determining the numerical simulation optimization scheme for process parameters; S4. Simulating pressurized seepage during fracture propagation in energy storage fracturing; S5. Simulating post-fracturing seepage and production in wells; S6. Determining target process parameters with production capacity as the objective; S7. Repeating steps S4 to S6 until all target process parameters are determined.

[0037] This application can effectively extend the stable production period of fracturing oil recovery and significantly improve the recovery rate, making the overall construction parameters more scientific and reasonable.

[0038] Example 2

[0039] The method for designing energy storage fracturing process parameters in tight oil reservoirs according to this application includes the following steps: S1. Obtaining basic data of the target reservoir; S2. Conducting laboratory experiments to evaluate the performance of energy storage fracturing fluid; S3. Determining the numerical simulation optimization scheme for process parameters; S4. Simulating pressurized seepage during fracture propagation in energy storage fracturing; S5. Simulating post-fracturing seepage and production in wells; S6. Determining the optimal process parameters with production capacity as the target; S7. Repeating steps S4 to S6 until all optimal process parameters are determined.

[0040] The on-site process of energy storage fracturing is as follows: ① Pre-energy storage fracturing hydraulically opens the reservoir; ② Fracturing fluid continues to create fractures; ③ Fracturing fluid carries sand to support the fractures; ④ Displacement; ⑤ Well shut-in and seepage absorption; ⑥ Well opening, venting and flowback.

[0041] The basic data of the target reservoir in step S1 include: porosity, permeability, oil saturation, crude oil viscosity, reservoir thickness, formation pressure coefficient, maximum horizontal principal stress, minimum horizontal principal stress, rock elastic model, Poisson's ratio, tensile strength, and wetting contact angle.

[0042] The performance parameters of the accumulator fracturing fluid in step S2 include surface / interfacial tension, wetting properties, permeability damage rate, and oil displacement capacity.

[0043] Among these methods, surface tension was measured using a fully automated surface tension meter, and interfacial tension between the stored fracturing fluid and dehydrated crude oil was measured using a rotary titration interfacial tension meter. In the wetting performance evaluation experiment, the core was directly immersed in the stored fracturing fluid, dried, and the wetting contact angle was directly measured. The wetting contact angle before and after immersion was compared, and the change rate of the contact angle was calculated. In the permeability damage rate experiment, the permeability of the core was first measured by gas, then the core was displaced with stored fracturing fluid, and finally the permeability of the core was measured by gas again. The permeability damage rate was obtained by comparing the permeability before and after displacement. In the oil displacement capacity experiment, the basic data of the core were first measured, and the core was saturated with standard brine, then saturated with dehydrated kerosene, and finally displaced with stored fracturing fluid until the water content of the produced fluid reached more than 98%.

[0044] The requirements are met when the surface tension of the energy storage fracturing fluid is <50mN / m, the interfacial tension is <0.1mN / m, the contact angle change rate is >35%, the permeability damage rate is <30%, and the displacement recovery rate is >5%.

[0045] In step S3, the process parameters include the amount of energy storage fracturing fluid used, the discharge rate, and the well-keeping time. During the numerical simulation, the optimal parameters are determined sequentially according to the order of energy storage fracturing fluid usage, discharge rate, and well-keeping time. That is: with a fixed discharge rate and well-keeping time, the energy storage fracturing fluid usage is varied to determine the optimal energy storage fracturing fluid usage; with a fixed optimal energy storage fracturing fluid usage and well-keeping time, the discharge rate is varied to determine the optimal discharge rate; with a fixed optimal energy storage fracturing fluid usage and optimal discharge rate, the well-keeping time is varied to determine the optimal well-keeping time.

[0046] The method for simulating crack propagation in step S4 is the element splitting method, as detailed in the literature “Zhang Zhennan, Wang Yujie, Mou Jianye, et al. Numerical simulation of fully coupled hydraulic fracturing based on element splitting method [J]. Science in China: Technological Sciences, 2019, 049(006):716-724.” and “Zhang Zhennan, Zheng Hong, Ge Xiurun. Triangular element splitting method considering crack tip [J]. Science in China: Technological Sciences, 2013, 000(010):1136-1143.”.

[0047] The fracturing fluid adsorption process during fracture propagation is pressurized adsorption. The forces acting on the fracturing fluid in the matrix pores are capillary force, viscous resistance, and gravity. According to the force balance, its adsorption rate is:

[0048]

[0049] In the formula: This is the absorption rate, expressed in m / s; The viscosity of the energy storage fracturing fluid is expressed in Pa·s. The pore radius is in meters (m). Interfacial tension, in N / m; The wetting contact angle is expressed in rad. The pressure difference between the inside and outside of the capillary tube; Density of the energy storage fracturing fluid, in kg / m³ 3 ; This is the acceleration due to gravity, measured in m / s². 2 , The height of the fracturing fluid drawn into the capillary is expressed in meters (m).

[0050] The adsorption rate at different locations can be calculated based on the matrix pore pressure distribution and reservoir parameters during fracture propagation. The adsorption rate affects the matrix pore pressure distribution, so iterative solutions are required to obtain the matrix pore pressure distribution at different times and after fracture propagation.

[0051] Based on parameters such as crack width obtained after the crack propagation simulation, the crack conductivity can be further calculated using the cubic law.

[0052] In step S5, the CMG software is used to establish a mechanism model to simulate the entire process of well simmering and production after energy storage fracturing. The initial pore pressure and fracture conductivity required in the calculation process are the pore pressure distribution and fracture conductivity after the fracture propagation is completed, as calculated in step S4.

[0053] This invention combines indoor experiments and numerical simulations to elevate the design of energy storage fracturing process parameters in tight oil reservoirs from an empirical stage to a quantitative design stage. Its application in key wells of tight oil reservoirs in Jiangsu Oilfield has yielded significant oil enhancement results. It demonstrates that replenishing formation energy before implementing large-scale sand fracturing with a temporary plugging and diversion technique, increasing fracture complexity and stimulation volume, can effectively extend the stable production period of fracturing-induced oil production. Simultaneously, the previously injected active water-based washing agent undergoes oil-water exchange with the formation crude oil, significantly improving recovery rates. This provides a new approach for the effective stimulation of difficult-to-access reserves and for increasing production and efficiency in old oil wells. Through quantitative simulation design, the entire construction parameters are made more scientific and reasonable, filling a gap in related domestic fields.

[0054] Example 3

[0055] In one specific embodiment, the target reservoir is a low-permeability tight reservoir with a permeability of 0.1 mD, a pressure coefficient of 0.85, and severely insufficient formation energy, requiring energy storage fracturing to improve single-well productivity. The remaining basic data of the target reservoir are as follows: porosity 5%, oil saturation 65%, crude oil viscosity 6 mPa·s, reservoir thickness 30 m, maximum horizontal principal stress 42 MPa, minimum horizontal principal stress 38 MPa, rock elastic modulus 30 GPa, Poisson's ratio 0.22, tensile strength 5 MPa, and wetting contact angle 82°.

[0056] To improve the effectiveness of energy storage fracturing, the preferred energy storage fracturing fluid system is: 0.3% oil displacement surfactant VBL-8 + 0.2% high-efficiency drag reducer FJZ-2 + 1% KCl. The surface tension of the system was measured using a fully automated surface tension meter, and was found to be 39 mN / m. The interfacial tension between the system and dehydrated crude oil was measured using a rotary titration interfacial tensiometer, and was found to be 0.093 mN / m. The wetting contact angle of the core before immersion was 82°, and after immersion it was 44°, with a contact angle change rate of 46.3%. The core permeability before displacement was 0.12 mD, and after displacement it was 0.10 mD, with a permeability loss rate of 16.7%. The improvement in recovery rate after displacement was 6.3%. Therefore, this system meets the requirements for energy storage fracturing in tight oil reservoirs.

[0057] The fracturing fluid dosage was changed to 1000 / 1500 / 2000 / 2500 / 3000 / 3500 / 4000m³. 3 Maintain a construction discharge volume of 8m³. 3 / min, well simmering time is 3d.

[0058] With a fracturing fluid usage of 1000m³ 3 Construction displacement is 8m 3 This explanation uses an example of a flow rate of / min and a well-clogging time of 3 days. The matrix pore pressure after the completion of the energy storage fracturing operation is calculated using the unit fracturing method and the permeation equation. Figure 2 The average fracture width was 1 mm, and the fracture conductivity was calculated to be 20 D·cm using the cubic law. The matrix pore pressure distribution and fracture conductivity data were imported into a mechanistic model established using CMG software, simulating an initial daily oil production of 7.2 t / d and a three-year cumulative oil production of 680 t. The three-year cumulative oil production under different storage fracturing fluid dosages was calculated using the above method. Figure 3 When the volume of energy storage fracturing fluid reaches 3500m³ 3 Subsequently, further increases in dosage did not significantly improve cumulative oil production; therefore, the optimal dosage of accumulator fracturing fluid is 3500 m³. 3 .

[0059] The construction displacement was changed to 2 / 4 / 8 / 12 / 14m. 3 / min, maintain the storage fracturing fluid volume at 3500m³. 3 The well-sinking time is 3 days. The cumulative oil production over three years under different drilling displacements is calculated according to steps S4 and S5. Figure 4 When the displacement reaches 12m 3 After reaching a certain displacement rate, further increasing the displacement resulted in a decrease in cumulative oil production. Therefore, the optimal operating displacement is 12 m³ / min. 3 / min.

[0060] The well shut-in time was changed to 1 / 2 / 3 / 4 / 5 / 6 days, while the energy storage fracturing fluid volume was kept at 3500 m³. 3 The construction discharge volume is 12m. 3 / min, the cumulative oil production over three years under different well-closing times was calculated according to steps S4 and S5, see [see details]. Figure 5 Once the well-sinking time reaches 4 days, further increasing the sinking time does not significantly increase the cumulative oil production. Therefore, the optimal well-sinking time is 4 days.

[0061] The optimal fracturing fluid dosage was finally determined to be 3500 m³. 3 The optimal construction discharge volume is 12m³. 3 / min, the optimal well-closing time is 4d.

[0062] This invention combines indoor experiments and numerical simulations to elevate the design of energy storage fracturing process parameters in tight oil reservoirs from an empirical stage to a quantitative design stage. Its application in key wells of tight oil reservoirs in Jiangsu Oilfield has yielded good oil enhancement results. It demonstrates that replenishing formation energy before implementing large-scale sand fracturing with a temporary plugging and diversion technique, increasing fracture complexity and stimulation volume, can effectively extend the stable production period of fracturing-induced oil enhancement. Simultaneously, the previously injected active water-based washing agent undergoes oil-water replacement with the formation crude oil, significantly improving recovery rates. This provides a new approach for the effective stimulation of difficult-to-access reserves and for increasing production and efficiency in old oil wells. Quantitative simulation design makes the entire construction parameters more scientific and reasonable.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for designing process parameters for energy storage fracturing in tight oil reservoirs, characterized in that, include: S1. Obtain basic data of the target reservoir; The basic data of the target reservoir in step S1 include: porosity, permeability, oil saturation, crude oil viscosity, reservoir thickness, formation pressure coefficient, maximum horizontal principal stress, minimum horizontal principal stress, rock elastic model, Poisson's ratio, tensile strength, and wetting contact angle. S2. Conduct indoor experiments to evaluate the performance of the storage fracturing fluid; the performance parameters of the storage fracturing fluid in step S2 include surface / interfacial tension, wetting properties, permeability damage rate, and oil displacement capacity; surface tension is measured using a fully automated surface tension meter, and the interfacial tension between the storage fracturing fluid and dehydrated crude oil is measured using a rotary titration interfacial tension meter; in the wetting properties evaluation experiment, the core is directly immersed in the storage fracturing fluid, and after drying, the wetting contact angle is directly measured, and the wetting contact angle before and after immersion is compared to calculate the contact angle change rate; in the permeability damage rate experiment, the permeability of the core is first measured by gas. Then, the core is displaced using energy-storing fracturing fluid, and finally the core permeability is measured by gasification. By comparing the permeability before and after displacement, the permeability damage rate can be obtained. In the oil displacement capacity experiment, the basic data of the core are first measured, and the core is saturated with standard brine, then saturated with dehydrated kerosene, and finally displaced with energy-storing fracturing fluid until the water content of the produced fluid reaches more than 98%. The requirements are met when the surface tension of the energy-storing fracturing fluid is <50mN / m, the interfacial tension is <0.1mN / m, the contact angle change rate is >35%, the permeability damage rate is <30%, and the increase in the degree of displacement and production is >5%. S3. Determine the numerical simulation optimization scheme for process parameters; the process parameters in step S3 include the amount of energy storage fracturing fluid used, the discharge rate, and the well-keeping time. During the numerical simulation, the target parameters are determined sequentially according to the order of energy storage fracturing fluid used, discharge rate, and well-keeping time, that is: set the discharge rate and well-keeping time, vary the amount of energy storage fracturing fluid used, and determine the optimal amount of energy storage fracturing fluid used; set the target amount of energy storage fracturing fluid used, set the well-keeping time, vary the discharge rate, and determine the target discharge rate; set the target amount of energy storage fracturing fluid used, set the target discharge rate, vary the well-keeping time, and determine the target well-keeping time. S4. Simulation of pressurized seepage during fracture propagation in energy storage fracturing; S5. Simulation of post-fracturing well sumption and production in energy storage fracturing; S6. Determine the target process parameters based on production capacity; S7. Repeat steps S4 to S6 until all target process parameters are determined.

2. The method for designing process parameters for energy storage fracturing in tight oil reservoirs according to claim 1, characterized in that, The method used to simulate crack propagation in step S4 is the element splitting method.

3. The method for designing energy storage fracturing process parameters for tight oil reservoirs according to any one of claims 1-2, characterized in that, In step S4, the fracturing fluid adsorption process during fracture propagation is pressurized adsorption. The forces acting on the fracturing fluid in the matrix pores are capillary force, viscous resistance, and gravity. Based on the force balance, its adsorption rate is: In the formula: This is the absorption rate, expressed in m / s; The viscosity of the energy storage fracturing fluid is expressed in Pa·s. The pore radius is in meters (m). Interfacial tension, in N / m; The wetting contact angle is expressed in rad. The pressure difference between the inside and outside of the capillary tube; Density of the energy storage fracturing fluid, in kg / m³ 3 ; This is the acceleration due to gravity, measured in m / s². 2 , The height of the fracturing fluid drawn into the capillary is expressed in meters (m).

4. The method for designing process parameters for energy storage fracturing in tight oil reservoirs according to any one of claims 1-2, characterized in that, In step S4, the adsorption rate at different locations can be calculated based on the matrix pore pressure distribution and reservoir parameters during the fracture propagation process. The adsorption rate affects the matrix pore pressure distribution, so iterative solution is required to obtain the matrix pore pressure distribution at different times and after the fracture propagation ends.

5. The method for designing process parameters for energy storage fracturing in tight oil reservoirs according to any one of claims 1-2, characterized in that, In step S4, the crack conductivity is further calculated using the cubic law based on the crack width parameters obtained after the crack propagation simulation.

6. The method for designing process parameters for energy storage fracturing in tight oil reservoirs according to any one of claims 1-2, characterized in that, In step S5, the CMG software is used to establish a mechanism model to simulate the entire process of well simmering and production after energy storage fracturing. The initial pore pressure and fracture conductivity required in the calculation process are the pore pressure distribution and fracture conductivity after the fracture propagation is completed, as calculated in step S4.

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